Nanometer Wars: Athlon 64 versus...Athlon 64

Review: Today, you can buy two variants of the Athlon 64 processor 3500+. One is built using AMD's older 130nm process, the other manufactured on 90nm. Do these make a real-world difference?

Last fall, AMD quietly started shipping Athlon 64 processors built on a 90nm process developed with IBM. Using its own product naming system, the 90nm processors top out with the Athlon 64 3500+, which clocks at 2.2GHz and contains 512KB of L2 cache. Codenamed "Winchester," the 90nm 3500+ is a scant 84 mm2, compared to 144 mm2 using the older 130nm manufacturing process.

A smaller die size lets AMD build more CPU dies onto a single wafer, which theoretically reduces the cost to manufacture the CPU. It's never quite that simple, of course, because the cost of developing the new manufacturing process needs to be amortized.

Another theoretical advantage should be lower thermal dissipation at the same clock speed. As we've seen with the Prescott-based Pentium 4 processors, this isn't always the case. At clock rates exceeding 3.2GHz, the Prescott's thermal output climbs in a sort of hockey-stick function, going from 84W at 3.2GHz to 115W at 3.6GHz. Interestingly, AMD has not tried to push their 90nm CPUs past the 3500+ (2.2GHz mark) to date.

With the 3500+, AMD has managed to reduce overall thermal output by a noticeable margin. Winchester's voltage requirements have been reduced slightly, to 1.4v from 1.5v for the 130nm part. The rated nominal thermal output is 67W, versus 89W for 130nm. But does this reduction translate into real world advantage? We dug out our Fluke digital voltmeter and a thermocouple and decided to find out. Continued...

We've been fans of small form factor PCs for some time now, and the recent release of the Shuttle SN95G5 gives us an opportunity to test the differences between the two generations of CPUs in an environment where space is tight and heat dissipation is a big challenge. We loaded up our SN95G5 with the following hardware:

We used a Fluke 189 digital multimeter with the TK80 thermocouple attachment to take temperature readings. We mounted the thermocouple onto the external top heat sink surface, which allowed us some idea of the temperature of the CPU, plus some ambient surrounding temperature in the case. The SN95G5 offers pretty good heat dissipation for such a restricted package, but can still get pretty warm when running a CPU and graphics intensive game.

The thermocouple was attached to the heat sink, in the lower trough between two center fins, and attached with a piece of thermal tape. We used Arctic Silver 5 between the copper heat sink surface and the heat spreader on the Athlon 64. We were also careful to use the same amount of heatsink paste and spread it evenly. In addition, the heat sink and CPU surfaces were cleaned with solvent when we swapped in the CPU. The 130nm version was tested first, then the 90nm product. The thermocouple wire was routed through vent holes in the SN95G5 case, and the case top was installed as it would be under normal use. The ambient air temperature was 68.5 degrees F.

Testing took the better part of a day, as stable temperature readings would typically take about 30 minutes to an hour to achieve, and we took two sets of readings and report the average. Let's take a look at the results.

It's clear that the 3500+ on 90nm runs cooler, as the difference in rated thermal output would indicate. Looking at the temperature chart, it's tough to really see what it means, so let's now consider the percentage difference.

The 3DMark05 test ostensibly measures CPU differences using game-like 3D scenes. However, even the low-res CPU tests use pixel shaders when running the tests, so the GPU kicks in. The Prime95 tests, on the other hand, are heavily CPU bound. So it's natural that a larger difference would show up when running those tests. There's even a minor, but repeatable, difference running at idle. (Note that we didn't have AMD's "Cool and Quiet" technology enabled.) Continued...

So the 90nm Athlon 64 3500+ runs cooler than the 130nm variant. At first blush, that shouldn't be a surprise. But when we recall concerns about Intel's thermal problems with Prescott, maybe it should be a surprise.

Recently, Ed Stroglio at Overclockers.com speculated that AMD realized that pushing the clock rate higher might result in the same sort of hockey-stick thermal performance as seen with Intel's 90nm Pentium 4's. As evidence, he points to IBM's troubles in pushing up the clock rate of the most recent 90nm Power PC processors. AMD's process is based on IBM's technology, so perhaps it's no surprise that AMD is holding back the clock rates. Their second-generation 90nm process is slated to come on line in early 2005. According to AMD's own roadmap, high-end CPUs manufactured at 90nm should ship sometime in the first half of 2005.

Today, however, the Athlon 64 3500+ is still a pretty solid CPU. If you get one, though, try to find a 90nm version. Cooler is better in the PC universe, and the new version is definitely cooler running.

Trails the equivalent Pentium 4 in most other applications; 512KB L2 cache

Summary:

If you want a great CPU for PC gaming at a reasonable price, the 3500+ is worth a look. Great for small form factor PCs

Price:

$265

Score:

Keep up to date on CPUs in our CPUs and Memory section.

Loyd Case came to computing by way of physical chemistry. He began modestly on a DEC PDP-11 by learning the intricacies of the TROFF text formatter while working on his master's thesis. After a brief, painful stint as an analytical chemist, he took over a laboratory network at Lockheed in the early 80's and never looked back. His first 'real' computer was an HP 1000 RTE-6/VM system.

In 1988, he figured out that building his own PC was vastly more interesting than buying off-the-shelf systems ad he ditched his aging Compaq portable. The Sony 3.5-inch floppy drive from his first homebrew rig is still running today. Since then, he's done some programming, been a systems engineer for Hewlett-Packard, worked in technical marketing in the workstation biz, and even dabbled in 3-D modeling and Web design during the Web's early years.

Loyd was also bitten by the writing bug at a very early age, and even has dim memories of reading his creative efforts to his third grade class. Later, he wrote for various user group magazines, culminating in a near-career ending incident at his employer when a humor-impaired senior manager took exception at one of his more flippant efforts. In 1994, Loyd took on the task of writing the first roundup of PC graphics cards for Computer Gaming World -- the first ever written specifically for computer gamers. A year later, Mike Weksler, then tech editor at Computer Gaming World, twisted his arm and forced him to start writing CGW's tech column. The gaming world -- and Loyd -- has never quite recovered despite repeated efforts to find a normal job. Now he's busy with the whole fatherhood thing, working hard to turn his two daughters into avid gamers. When he doesn't have his head buried inside a PC, he dabbles in downhill skiing, military history and home theater.

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